1. Field of the Invention
This invention relates generally to signal delay, and more particularly to delay line circuitry.
2. Description of the Related Art
A delay line is a circuit designed to introduce a calculated time delay into the transmission of a signal. Delay lines may be used for different purposes including, for example, phase shifting, time shifting, etc. Most delay line applications require that delay lines be tuned or adjusted. For example, in the field of microwave phase shifting, creation of accurate microwave phase shifters and delay lines requires labor to tune a device during test. Without tuning, the tolerances in the dielectric of the material and manufacturing process make it impossible to create accurate and repeatable designs. There are many different types of delay lines and delay line adjustment techniques may vary according to topology. For example, when working with coaxial cables, mircrostrip, stripline and coplanar waveguide technologies, common delay techniques that have been employed include use of tuning stubs, adding to or trimming transmission lines, adding capacitors, etc. Such techniques are relatively labor intensive and time consuming.
Phased array apparatus are employed in a variety of applications for transmitting and receiving radar and other types of radio-frequency (RF) signals, and may be implemented in a variety of geometric array configurations. Examples of array configurations include linear arrays, two-dimensional arrays, planar arrays, rectangular arrays and conformal arrays. Phase shifting devices have been used to alter the phase of signals transmitted or received by individual phased array elements relative to each other in order to control the directional orientation of signals transmitted or received by the array. Examples of phase shifting devices include digital phase shifting devices (e.g., diode phase shifter using switched-line, hybrid-coupled and loaded-line) and analog phase shifting devices that are digitally controlled (e.g., ferrite phase shifter). In the latter case, phase shifters using ferrite materials are found in high power applications, but they are generally relatively large in size. Ferrite phase shifters utilize the magnetic hysteresis of a ferrite material to provide a phase shift when a bias field is applied to the material. However, a full characterization of the ferrite material must be made since the hysteresis curves are unique for each device made out of the same ferrite material.